Should you add batteries to your solar array?

Editor's Note: Scientific American's George Musser will be chronicling his experiences installing solar panels in Solar at Home (formerly 60-Second Solar). Read his introduction here and see all posts here.

Once upon a time, all solar arrays were off-grid. That was the whole point: solar enthusiasts wanted to, or had to, generate their own electricity rather than rely on a utility. They installed banks of batteries to store power for use when the sun went down. Today, with net-metering, we let the grid "store" the power for us. That said, batteries have not gone away entirely.

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How the grid stores power is a fascinating subject in its own right. In essence, the electricity from a home solar panel or wind turbine flows into the transmission lines and reduces the load on power plants. The line voltage changes ever so slightly and the dynamos spin up or down to compensate. If you're familiar with the basics of electricity, you might enjoy this discussion by physicist and engineer John Denker. For a longer discussion that delves into the history of the grid and the challenges of preventing blackouts, see Massoud Amin and Phil Schewe's article in our May 2007 issue or Schewe's book The Grid: A Journey Through the Heart of Our Electrified World.

As more people install solar panels, their power output will eventually overwhelm the grid's existing mechanisms and utilities will need some kind of energy storage system such as compressed air. But that is a longer-term problem and probably won't require batteries in individual buildings.

Nonetheless, batteries can still play a role in a home solar system by providing standby power during blackouts. Our street in suburban New Jersey has an inordinate number of blackouts -- and whenever we do, we lose our heat. It wouldn't take long in midwinter for our house to become uninhabitable. You might think that at least we'd get power by day, through the solar array, but no: when the grid shuts down, so does the inverter that injects the array's power into our household wiring. The panels dangle there uselessly.

Home Power magazine had an excellent discussion of the pros and cons of batteries, including sample cost figures. The main disadvantages are added cost and complexity. Not only do you need to buy batteries and find a place to put them, you need to install an electronic controller to charge and discharge the batteries in an optimal way depending on their chemistry. Physics Today had a great article last year on a DIY solar array which discussed how charge controllers work. I personally find them a fascinating technology, but even my enthusiasm wanes when I think about adding one more thing that could go wrong.

One person responding to my call for stories about solar installations, Ken Klatt of Mequon, Wisc., told me of his struggles with a DIY grid-tied system with battery backup. Here's what he had to say (somewhat edited by me):

The system produces 380 watts with a planned maximum of 1,000 watts. Batteries store power during non-sun times (a challenge in Wisconsin). The entire system is off-grid (when it can be). It is monitored by a special low-power computer (Shiva Plug) that switches to grid-power when power levels drop below 40 percent available. During the months from June to September, the computer runs off-grid without major issues (there are a few planned outages where power is switched to grid power). The site data is available online.

I started out in summer 2005 with the "What can I do for $500" -- and have now spent approximately $5K. The only subsidies I took advantage of were Federal tax refunds for solar power generation.

I get frustrated with websites that tout "green". You see a solar-panel mount with a clear view of the south, no neighbors complaining, no trees, etc., blocking the sun. I have had enough problems to fill volumes -- neighbors, tree shading, weather, mice chewing wires, interconnections, panel locations, charge controller communications, communication protocols -- the list seems endless, not to mention the expenses. I'm looking at greater than a 10-year payback period.

The issues fall into three groups, electrical, weather, and social (people):

I live in a suburb, and zoning laws are unclear or unstated. Positioning the panels was a major headache; there were no perfect locations available that are not shaded, etc.

The charge controller I bought was defective and had to be sent back to the factory.

The second year, the inverter failed and had to replaced.

I have had other hardware issues such as loose connections in the battery array, in the solar-panel terminal, and in the wire nuts (because the electrical wire supplied was not tinned).

The next-door neighbor complained about the look of the solar panels and made numerous requests to remove them. Last month, I relented and mounted the panels on the ground rather than the roof.

The entire month of October 2009 was cloudy except for two or three days and my batteries may have been damaged as a result.

The first winter, a storm layered the panels with ice and snow. It took three weeks to clear, during which time I had no safe access to the roof. When I was able to climb up and inspect the array, I found wind damage to the panel mounts. Similar problems have occurred in subsequent winters.

I created my own software drivers for the Solar Charge controller, running under Linux. I had trouble with the communications protocols and eventually had to install third-party hardware to resolve the issue.

Anyone who has undertaken any sort of DIY project will empathize. Hang in there, Ken. Most people have it easier, since they hire installers -- though, of course, contractors have their own issues. Solar is still an emerging technology and we can expect hiccups. Over time, the early adopters will pave the way for the rest of us.

ABOUT THE AUTHOR(S)

George Musser

George Musser is a contributing editor at Scientific American. He focuses on space science and fundamental physics, ranging from particles to planets to parallel universes. Musser completed his undergraduate studies in electrical engineering and mathematics at Brown University and his graduate studies in planetary science at Cornell University, where he was a National Science Foundation Graduate Research Fellow. Prior to joining Scientific American, Musser served as editor of Mercury magazine and of The Universe in the Classroom tutorial series for K–12 teachers at the Astronomical Society of the Pacific, a science and science-education nonprofit based in San Francisco. He is also the author of

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